Answer

The make function in Go is used exclusively for initializing objects of types: slice, map, and channel. It allocates the necessary data structure and returns a ready-to-use object (not a pointer!).

Examples:

s := make([]int, 5, 10)    // slice of length 5, capacity 10
m := make(map[string]int)  // empty map
ch := make(chan int, 2)    // buffered channel of 2

Details:

• For slice, parameters: length (len) and (optionally) capacity (cap).
• For map and chan — only (optional) capacity (initial size/buffer).
• The make function returns an already initialized object, ready for use.
• For other types (struct, array) make is not used; they are initialized using literals or new (which returns a pointer to a zero value).

Comparison with new:

• new(T) returns *T, where all fields are zero.
• make(T) returns T only for three types: slice, map, chan.

Trick Question

Can you get a working map through new instead of make?

m := new(map[string]int)
(*m)["a"] = 1 // What will happen?

Many believe this is correct, but it will cause a panic at runtime: assignment to entry in nil map. Because the variable *m holds nil!

Correct: use make:

m := make(map[string]int)
m["a"] = 1 // OK

Examples of real errors due to lack of understanding of the nuances

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Story

In a microservice for cache storage, a map was created via var cache map[string]interface{} without initializing make, which caused a panic in production when writing, with confusing stack traces. The problem was found only after code analysis: the map was nil.

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Story

When writing a data pipeline, the buffer in the channel was forgotten and created via make(chan int). As a result, goroutines got stuck waiting for reading, although asynchronous exchange was expected. The error was noticed only during large-scale testing.

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Story

In a project where initialization was done via new, some developers tried to use new([]int) instead of make([]int, 10), ultimately getting a pointer to a nil slice and runtime panic on the first write attempts.